1. Field of the Invention
The present invention relates to photoelectric conversion substrates, photoelectric conversion apparatuses, radiation detection substrates, and radiation detection apparatuses for use in medical diagnostic imaging apparatuses, non-destructive inspection apparatuses, analysis apparatuses using radiation, and the like. In this specification, radiation includes electromagnetic waves like visible light, X-rays, α-rays, β-rays, γ-rays, etc.
2. Description of the Related Art
In general, conventional medical diagnostic imaging can be classified into two types: general imaging for obtaining still images, such as X-ray images, and fluoroscopic imaging for obtaining dynamic images. The type of imaging and an imaging apparatus to be used are selected as necessary.
In conventional general imaging, two methods described below are mainly used. One of the two methods is a screen-film imaging (hereafter abbreviated as SF imaging) method in which imaging is performed by film exposure, development, and fixing using a screen film obtained by combining a fluorescent plate and a film. The other method is a computed radiography imaging (hereafter abbreviated as CR imaging) method in which a radiographic image is recorded on a photostimulable phosphor plate as a latent image. Optical information corresponding to the latent image is output by scanning the photostimulable phosphor plate with a laser, and the output optical information is read out with a sensor. However, general imaging has a problem in that processes for obtaining the radiographic image are complex. In addition, although it is possible to convert the obtained radiographic image into digital data, the radiographic image is secondarily digitized in such a case and it takes a long time to obtain a digitized radiographic image.
In conventional fluoroscopic imaging, an image intensifier imaging (hereafter abbreviated as I.I. imaging) method using a fluorescent material and an electron tube is mainly used. However, conventional fluoroscopic imaging has a problem in that the size of the device is large since the electron tube is used. In addition, since the electron tube is used, view area (detection area) is small and it is difficult to obtain an image of a large area. In addition, there is also a problem that the resolution of the obtained image is low since the electron tube is used.
Accordingly, sensor panels in which pixels including conversion elements for converting radiation or light from a fluorescent material into electric charges and switching elements are arranged on a substrate in a two-dimensional matrix pattern have recently been attracting attention. In particular, flat panel detectors (hereafter abbreviated as FPD) in which pixels having conversion elements constructed of non-single crystal semiconductor, such as amorphous silicon (hereafter abbreviated as a-Si), and thin-film transistors (hereafter abbreviated as TFT) constructed of non-single crystal semiconductor are arranged on an insulating substrate in a two-dimensional matrix pattern have been attracting attention.
In the FPD, radiation having image information is converted into electric charges by the conversion elements, and the thus obtained electric charges are read out by the switching elements, so that electrical signals based on the image information can be obtained. Accordingly, the image information can be obtained directly from the FPD as digital signal information, and the image data can be easily stored, processed, transmitted, etc. Therefore, application of the radiographic image information can be increased. Although the characteristics, such as sensitivity, of the FPD can vary depending on imaging conditions, it is confirmed that the level of the characteristics of the FPD is the same as or higher than those of the SF imaging method and the CR imaging method. In addition, since the electrical signals representing the image information can be obtained directly from the FPD, the time required for obtaining an image can be reduced compared to those in the SF imaging method and the CR imaging method.
As an example of a FPD, a PIN-FPD including a sensor panel in which pixels including PIN photodiodes made of a-Si and TFTs are arranged in a two-dimensional matrix pattern is known. The PIN-FPD has a laminated structure in which a layer forming the PIN photodiodes is laminated on a layer forming the TFTs on a substrate. In addition, a MIS-FPD including a sensor panel in which pixels including MIS photosensors made of a-Si and TFTs are arranged in a two-dimensional matrix pattern is also known. The MIS-FPD has a planar structure in which the MIS photosensors are formed in the same layer as a layer forming the TFTs on a substrate. In addition, a MIS-FPD having a laminated structure in which a layer forming the MIS photosensors is laminated on a layer forming the TFTs on a substrate is also disclosed in, for example, U.S. Patent Application Publication No. 2003/0226974.
As an example of a FPD, the above-mentioned FPD discussed in U.S. Patent Application Publication No. 2003/0226974 will be explained below. Here, a structure in which pixels are arranged in a 3-by-3 matrix pattern will be described for simplicity.
FIG. 6 is a schematic equivalent circuit diagram illustrating an equivalent circuit of the conventional FPD discussed in U.S. Patent Application Publication No. 2003/0226974. FIG. 7 is a schematic plan view of a single pixel included in the conventional FPD discussed in U.S. Patent Application Publication No. 2003/0226974. FIG. 8 is a schematic sectional view of FIG. 7 taken along line VIII-VIII.
Light emitted from a wavelength converter in accordance with radiation incident thereon is converted into signal electric charges at each of a plurality of photoelectric conversion elements to which a bias voltage for photoelectric conversion is applied. A plurality of switching elements perform a transmission operation in accordance with drive signals applied to drive lines 103 by a drive circuit 107, and the signal electric charges obtained by the photoelectric conversion elements 101 are read out in parallel by a signal-processing circuit 106 via signal lines 104. The signal electric charges read out in parallel are converted into a serial signal by the signal-processing circuit 106, and the thus obtained serial signal is converted from analog to digital by an analog-to-digital (A/D) converter 108 and is then output. Accordingly, an image signal for a single image corresponding to the incident radiation that represents image information can be obtained.
In the above-described radiation detection apparatus using the FPD, the drive lines 103 are connected to the drive circuit 107 for applying the drive signals to gate electrodes of the switching elements 102 arranged in the row direction. In addition, the signal lines 104 are connected to the signal-processing circuit 106 for processing the signal electric charges generated by the photoelectric conversion elements 101 and transmitted from source or drain electrodes of the switching elements 102 arranged in the column direction. In addition, bias lines 105 are connected to a bias power source 109 having a first voltage for causing the photoelectric conversion elements 101 to perform photoelectric conversion and a second voltage for applying a bias for setting the photoelectric conversion elements 101 to an initial state. The electrical connections between the lines and the external circuits are provided by terminal elements provided on the lines at one end thereof. For example, terminal elements included in a radiation detection apparatus using a FPD discussed in Japanese Patent Laid-Open No. 2003-319270 will be described below.
A protective layer that covers the photoelectric conversion elements and the switching elements is removed in the entire area outside the pixel area so as to form a connection area (open area), and the terminal elements are connected to respective integrated circuits (ICs) in the contact area.
As described in, for example, International Patent Application Publication No. WO98/32179, in the radiation detection apparatus to which the ICs are connected, each of the ICs on an insulating substrate is covered by a sealing member (not shown) and is protected from the outside.
However, in the above-described radiation detection apparatus using the FPD, there is a possibility that corrosion of the terminal elements will occur. More specifically, since the protective layer is removed in the entire connection area and the terminal elements are not covered, the terminal elements are easily contaminated by moisture and impurities in the atmosphere. As discussed in International Patent Application Publication No. WO98/32179, each of the terminal elements is covered by a sealing member. However, moisture and impurities from an interface between the sealing member and the insulating substrate cannot be blocked sufficiently. Therefore, contamination by moisture and impurities at side faces of each terminal element and an interface between the terminal element and the insulating substrate cannot be suppressed sufficiently. In particular, in a radiation detection apparatus used for medical inspections, there is a possibility that rubbing alcohol, moisture, etc., will directly come into contact with the radiation detection apparatus. Accordingly, countermeasures for such a situation are demanded.
In addition, since the protective layer is removed in the entire connection area and the terminal elements are not covered, if conductive adhesive enters a gap between the adjacent terminal elements, there is a possibility that a short circuit will occur between the adjacent terminal elements. In such a case, a desired drive operation cannot be performed and an image cannot be obtained. Thus, there is a risk that reliability and manufacturing yield will be reduced.